Heating Performance Of A/C System, Checking: Notes

Special tools and workshop equipment required

Diagnostic operation system VAS 5051 A (or Vehicle Diagnosis and Service SystemVAS 5052).

NOTE:

If coolant circuit is not completely bled after filling, air may accumulate in heater core of A/C unit, thus reducing heating performance of A/C system, additional noises may occur or customer may complain of different air temperatures flowing out of vents at driver side and front passenger side at the same setting. For this malfunction, perform a long road test at increased engine speed (at least 10 minutes, engine speed greater than 2500 RPM). Select a low gear during the test to prevent excessive vehicle speed.
If customer complains of poor heating performance at specific engine speeds, check incorporation of heater core in A/C system in the coolant circuit. If both coolant hoses (supply and return) of engine are interchanged, coolant is flowing in the wrong direction through the heater core. Refer to HEATING PERFORMANCE, CHECKING .
In vehicles with a parking heater, check activation of Recirculation Pump -V55-, of parking heater as well as incorporation of parking heater in coolant circuit.
From MY 2010, this vehicle has a Start/Stop System for specific engines as optional equipment. If the vehicles has a manual climate control system, then, depending on the setting on the A/C Control Module -J301- (for example, the heater is on) the Stop function will prevent the engine from being started again as soon as there is a request for heating. In the cooling mode the Stop function is not limited by the A/C control module. On vehicles with an automatic climate control system, Climatronic Control Module -J255- prevents the Stop function, depending on the setting. If, for example, defrost is selected, the Stop Function is not possible or will be interrupted and the engine will start. The same applies in the case of heating and cooling. The difference between the selected and actual temperature is greater than a specified value shown using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
If the vehicle has the Start/Stop System, there is no additional coolant pump. An electric coolant pump may be present depending on the vehicle engine, which is controlled by an engine control module. Refer to GENERAL INFORMATION and refer to COOLANT PUMP AND COOLANT THERMOSTAT ASSEMBLY OVERVIEW and Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
Climatronic control module, part number 8P0 820 043 starting with index BM sends the request to control the electric coolant pump only with the correct adaptation on the databus. Make sure a Climatronic control module with the index BM is installed using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".